Organic Thin Film Ink Compositions and Methods

ABSTRACT

The present teachings relate to various embodiments of an ink composition, which once printed and cured forms an organic thin film on a substrate such as, but not limited by, an OLED device substrate. Various embodiments of the ink can be printed using an industrial inkjet printing system that can be housed in a gas enclosure, which gas enclosure defines an interior that has a controlled environment maintained as an inert and substantially low-particle process environment. Patterned printing of an organic thin film on a substrate, for example, but not limited by, an OLED device substrate, in such a controlled environment can ensure a high-volume, high yield process for a variety of OLED devices.

RELATED APPLICATIONS

The present application claims priority to: U.S. provisional patentapplication No. 62/029,228, filed on Jul. 25, 2014; U.S. provisionalpatent application No. 62/035,600, filed on Aug. 11, 2014; and U.S.provisional patent application No. 62/084,751, filed on Nov. 26, 2014,the entire contents of which are incorporated herein by reference.

FIELD

The present teachings relate to various embodiments of an inkcomposition, and a polymeric thin film formed on a substrate, such as,but not limited by, an OLED device substrate. Various embodiments of theink can be printed using an industrial inkjet printing system that canbe housed in a gas enclosure, which gas enclosure defines an interiorthat has a controlled environment maintained as an inert andsubstantially low-particle process environment.

Overview

Interest in the potential of organic light-emitting diode (OLED) displaytechnology has been driven by OLED display technology attributes thatinclude demonstration of display panels that have highly saturatedcolors, are high-contrast, ultrathin, fast-responding, and energyefficient. Additionally, a variety of substrate materials, includingflexible polymeric materials, can be used in the fabrication of OLEDdisplay technology. Though the demonstration of displays for smallscreen applications, primarily for cell phones, has served to emphasizethe potential of the technology, challenges remain in scaling highvolume manufacturing across a range of substrate formats in high yield.

With respect to scaling of formats, a Gen 5.5 substrate has dimensionsof about 130 cm×150 cm and can yield about eight 26″ flat paneldisplays. In comparison, larger format substrates can include using Gen7.5 and Gen 8.5 mother glass substrate sizes. A Gen 7.5 mother glass hasdimensions of about 195 cm×225 cm, and can be cut into eight 42″ or six47″ flat panel displays per substrate. The mother glass used in Gen 8.5is approximately 220 cm×250 cm, and can be cut to six 55″ or eight 46″flat panel displays per substrate. One indication of the challenges thatremain in scaling of OLED display manufacturing to larger formats isthat the high-volume manufacture of OLED displays in high yield onsubstrates larger than Gen 5.5 substrates has proven to be substantiallychallenging.

In principle, an OLED device may be manufactured by the printing ofvarious organic thin films, as well as other materials, on a substrateusing an OLED printing system. Such organic materials can be susceptibleto damage by oxidation and other chemical processes. As such, printingof various organic stack layers in an inert environment is indicated.Additionally, the need for a substantially particle-free environment isindicated in order to realize a high-yield manufacturing process. Inaddition to the printing of various layers of an OLED stack into aplurality of discrete pixel locations, patterned area printing using anindustrial inkjet system can be done. For example, during fabrication ofan OLED device, inkjet printing of various encapsulation layers can bedone. Given the sensitivity of the various organic materials of an OLEDstack that can be damaged by oxidation and other chemical processes, aswell as defects due to particulate matter in a printed thin layer of amaterial, the patterned printing of an encapsulation layer in an inert,substantially particle free environment is also indicated.

However, housing an OLED printing system in a fashion that can be scaledfor various substrate sizes and can be done in an inert, substantiallylow-particle printing environment can present a variety of engineeringchallenges. Manufacturing tools for high throughput large-formatsubstrate printing, for example, such as printing of Gen 7.5 and Gen 8.5substrates, require substantially large facilities. Accordingly,maintaining a large facility under an inert atmosphere, requiring gaspurification to remove reactive atmospheric species, such as water vaporand oxygen, as well as organic solvent vapors, as well as maintaining asubstantially low-particle printing environment, has proven to besignificantly challenging.

As such, challenges remain in scaling high volume manufacturing of OLEDdisplay technology across a range of substrate formats in high yield.Accordingly, there exists a need for various embodiments a gas enclosuresystem of the present teachings that can house an OLED printing system,in an inert, substantially low-particle environment, and can be readilyscaled to provide for fabrication of OLED panels on a variety ofsubstrates sizes and substrate materials. Additionally, various gasenclosure systems of the present teachings can provide for ready accessto an OLED printing system from the exterior during processing and readyaccess to the interior for maintenance with minimal downtime.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the features and advantages of the presentdisclosure will be obtained by reference to the accompanying drawings,which are intended to illustrate, not limit, the present teachings.

FIG. 1 is a schematic section view of an optoelectronic device,illustrating various aspects of a fabrication.

FIG. 2(A) and FIG. 2(B) are film profiles of a polymeric thin filmformed on a substrate, according to various embodiments of compositions,systems and methods of the present teachings. FIG. 2(A) displays a filmof 8 μm thickness, which was printed without incorporating edgecompensation. FIG. 2(B) is a film of 16 μm thickness, which was printedusing edge compensation.

FIG. 3 is a flow diagram depicting a process for forming a polymericthin film on a substrate, according to various embodiments ofcompositions, systems and methods of the present teachings.

FIG. 4 is a front perspective view of view of a printing system tool inaccordance with various embodiments of the present teachings.

FIG. 5 is a schematic depiction of a UV curing module that can be usedin manufacturing a light emitting device.

FIG. 6 depicts an expanded iso perspective view of a printing system inaccordance with various embodiments of the present teachings.

FIG. 7 is an iso perspective view of a printing system in accordancewith various embodiments of the present teachings.

FIG. 8 is a schematic view of various embodiments of gas enclosureassembly and related system components the present teachings.

FIG. 9(A) is a graph of the drop volume as a function of jettingfrequency at 22° C. and 25° C. for a spreading modifier.

FIG. 9(B) is a graph of the drop velocity as a function of jettingfrequency at 22° C. and 25° C. for a spreading modifier.

FIG. 9(C) is a graph of the drop trajectory as a function of jettingfrequency at 22° C. and 25° C. for a spreading modifier.

FIG. 10(A) is a graph of the drop volume variation as a function ofjetting frequency at 22° C. and 25° C. for a spreading modifier.

FIG. 10(B) is a graph of the drop velocity variation as a function ofjetting frequency at 22° C. and 25° C. for a spreading modifier.

FIG. 11(A) is a graph of the ink drop velocity as a function of jettingfrequency at 25° C. for an ink composition.

FIG. 11(B) is a graph of the ink drop volume as a function of jettingfrequency at 25° C. for an ink composition.

FIG. 11(C) is a graph of the ink drop trajectory as a function ofjetting frequency at 25° C. for an ink composition.

FIG. 12 is a graph of the volume change of the printed ink compositionsthat occurs upon curing as a function of photoinitiator concentration.

FIG. 13 is a graph showing the correlation between weight loss andphotoinitiator concentration for a film cured at 120° C., as measured bythermogravimetric analysis.

DETAILED DESCRIPTION OF THE DISCLOSURE

The present teachings relate to various embodiments of a inkcomposition, which once printed and cured forms a polymeric thin film ona substrate, such as, but not limited by, an OLED device substrate.Various embodiments of the ink can be printed using an industrial inkjetprinting system that can be housed in a gas enclosure, which gasenclosure defines an interior that has a controlled environmentmaintained as an inert and substantially low-particle processenvironment. Patterned printing of an organic thin film on a substrate,for example, but not limited by, an OLED device substrate, in such acontrolled environment can ensure a high-volume, high yield process fora variety of OLED devices.

It is contemplated that a wide variety of ink formulations can beprinted within the inert, substantially low-particle environment ofvarious embodiments of a gas enclosure system of the present teachings.During the manufacture of an OLED display, an OLED pixel can be formedto include an OLED film stack, which can emit light of a specific peakwavelength when a voltage is applied. An OLED film stack structurebetween an anode and a cathode can include a hole injection layer (HIL),a hole transport layer (HTL), an emissive layer (EL), an electrontransport layer (ETL) and an electron injection layer (EIL). In someembodiments of an OLED film stack structure, an electron transport layer(ETL) can be combined with an electron injection layer (EIL) to form anETL/EIL layer. According to the present teachings, various inkformulations for an EL for various color pixel EL films of an OLED filmstack can be printed using inkjet printing. Additionally, for example,but not limited by, the HIL, HTL, EML, and ETL/EIL layers can have inkformulations that can be printed using inkjet printing.

As will be discussed in more detail subsequently herein, it is furthercontemplated that an organic encapsulation layer can be printed on anOLED panel using inkjet printing. An encapsulation ink can comprise apolymer or polymer component, for example, but not limited by, variouspolyethylene glycol monomer materials, an acrylate, such as a mono- ormultidentate acrylate, a methacrylate, such as a mono- or multidentatemethacrylate, or other material, as well as copolymers and mixturesthereof, which can be cured using thermal processing (e.g. bake), UVexposure, and combinations thereof. As used herein polymer and copolymercan include any form of a polymer component that can be formulated intoan ink and cured on a substrate to form an organic encapsulation layer.Such polymeric components can include polymers and copolymers, as wellas precursors thereof, for example, but not limited by, monomers,oligomers, and resins. According to the present teachings, inkjetprinting can provide several advantages. First, a range of vacuumprocessing operations can be eliminated because such inkjet-basedfabrication can be performed at atmospheric pressure. Additionally,during an inkjet printing process, an organic encapsulation layer can belocalized to cover portions of an OLED substrate over and proximal to anactive region, to effectively encapsulate an active region, includinglateral edges of the active region. The targeted patterning using inkjetprinting results in eliminating material waste, as well as eliminatingadditional processing typically required to achieve patterning of anorganic layer.

Organic Thin Film Ink Compositions and Methods

Various embodiments of an organic thin layer ink composition of thepresent teachings can be printed, for example, but not limited by, on anoptoelectronic device, such as a wide number of OLED devices, to form anorganic encapsulation layer. According to various embodiments ofcompositions and methods, once cured, the resulting polymeric thin filmcan provide a fluid barrier, as well as providing planarization of apreviously fabricated inorganic encapsulation layer, and additionallyproviding flexibility desired from an organic encapsulation layer. Thefluid barriers can prevent or reduce the permeation of, for example,water and/or oxygen into the OLED devices.

As depicted in the schematic section view of FIG. 1, for optoelectronicdevice 50, a substrate 52 can be provided. Various embodiments of asubstrate can include one or more of a thin silica-based glass, as wellas any of a number of flexible polymeric materials. For example,substrate 52 can be transparent, such as for use in a bottom-emittingoptoelectronic device configuration. One or more layers associated withan OLED stack, such as various organic or other material can bedeposited, inkjet printed, or otherwise formed upon the substrate toprovide an active region 54, such as to provide electroluminescentregion. Note that active region 54 in FIG. 1 is illustratedschematically as a single block, but can in detail further include aregion having complex topology or structure with multiple discretedevices and film layers. In an example, 50 can include an OLED device,such as comprising an emissive layer, or other layers, coupled to ananode electrode and a cathode electrode. The phrase “active” need notimply any requirement of amplification of electrical energy ortransistor activity, and can refer generally to a region whereinoptoelectrical activity (e.g., light emission) can occur. Accordingly,active region 54 can be included as a portion of an active matrix OLEDor a passive matrix OLED device.

Respective layers included in an OLED device, such as in the activeregion 54, can be on the order of tens or hundreds of nanometers (nm)thick, or less. Additional organic layers that are not active in theoptoelectronic action of the OLED device can be included, and suchlayers can be on the order of microns thick, or less. An anode electrodeor a cathode electrode can be coupled to or can include electrodeportion 56 that is laterally offset along the substrate 52 from theactive region 54. As will be discussed in more detail herein, the activeregion 54 of the device 50 can include materials that degrade in thepresence of prolonged exposure to various reactive species gaseousspecies, such as, but not limited by, water, oxygen, as well as varioussolvent vapors from device processing. Such degradation can impactstability and reliability.

As depicted in FIG. 1, an inorganic layer 60A can be provided for device50, such as deposited or otherwise formed on active region 54. Forexample, the inorganic layer can be blanket coated (e.g., deposited)over an entirety, or substantially an entirety of a surface of thesubstrate 52, including active region 54. Examples of inorganicmaterials useful for fabricating inorganic layer 60A can include variousoxides, such as one or more of Al₂O₃, TiO₂, HfO₂, SiO_(X)N_(Y) or one ormore other materials. Organic layer 62A can be printed, using forexample, inkjet printing. For example, as previous generally discussedherein organic layer 62A can be printed using an organic thin layer inkthat can include various polymer materials can are curable using one ormore of a thermal (e.g., bake) or ultraviolet exposure technique, andonce cured can form polymeric thin film, such as organic layer 62A.Organic layer 62A can serve as one or more of a planarization layer toplanarize and mechanically protect the active region 54, or as a portionof an encapsulation stack that collectively serves to suppress orinhibit moisture or gas permeation into the active region 54. FIG. 1illustrates generally a multi-layer configuration of encapsulationmaterial layers having inorganic layer 60A such as including an oxide,and the organic layer 62A, such as including a polymer that can be usedto inhibit or suppress exposure of the active region 54 to reactivegases, such as, but not limited by, moisture or atmospheric gases. Asdepicted in FIG. 1, the multi-layer configuration can be repeated toinclude second inorganic layer 60B and second organic layer 62B. Variousadditional embodiments of encapsulation layers can be created to providethe mechanical and sealing properties desired for an optoelectronicdevice. For example, the order of the fabrication of the layers could bereversed, so that an organic encapsulation layer is first fabricated,followed by the fabrication of an inorganic layer. Additionally, more orless numbers of layers can be provided. For example, a structure havinginorganic layers 60A and 60B as shown, and a single organicencapsulation layer 62A can be fabricated.

For various embodiments of an organic thin layer ink of the presentteachings, can be composed of four starting materials. According to thepresent teachings, various compositions of an organic thin layer ink caninclude a polyethylene glycol dimethacrylate and/or a polyethyleneglycol diacrylate having a number average molecular weight in the rangefrom about 230 gm/mole to about 440 gm/mole. For example, the organicthin layer ink can include polyethylene glycol 200 dimethacrylate and/orpolyethylene glycol 200 diacrylate, having a number average molecularweight of about 330 gm/mole and having the generalized structure asshown below:

where n is on average 4 and R is independently selected from H andmethyl groups.

For various embodiments of an organic thin layer ink of the presentteachings, polyethylene glycol 200 dimethacrylate can be the primarycomponent of an ink formulation and can be between about 75-95 wt. % ofvarious embodiments of organic thin layer ink compositions.

In addition to polyethylene glycol 200 dimethacrylate, pentaerythritoltetraacrylate or pentaerythritol tetramethacrylate can be used as aprimary cross-linking agent. The term ‘primary’ is used here to indicatethat other components of the ink compositions also participate incrosslinking, although that is not their main functional purpose. Forvarious embodiments of an organic thin layer ink, can be between about4-10 wt. % of an ink formulation. A generalized structure forpentaerythritol tetraacrylate or pentaerythritol tetramethacrylate isshown below.

where R is independently selected from H and methyl groups.

According to the present teachings, a spreading modifier can be used totune the spreading characteristics of various embodiments of the organicthin layer ink compositions. The spreading modifier is a liquid having alower surface tension than the polyethylene glycol dimethacrylate of theink composition at the printing temperatures. By way of illustration,various embodiments of the ink compositions comprise a spreadingmodifier having a viscosity in the range from about 14 to about 18 cpsat 22° C. and a surface tension in the range from about 35 to 39dynes/cm at 22° C. This includes embodiments of the ink compositionsthat comprise a spreading modifier having a viscosity in the range fromabout 14 to about 16 cps at 22° C. and a surface tension in the rangefrom about 35 to 38 dynes/cm at 22° C. Methods for measuring viscositiesand surface tensions are well known and include the use of commerciallyavailable rheometers (e.g., a DV-I Prime Brookfield rheometer) andtensiometers (e.g., a SITA bubble pressure tensiometer). In someembodiments of the ink compositions, the spreading modifier comprises amultifunctional, such as difunctional, acrylate monomer or oligomer ormethacrylate monomer or oligomer. Acrylate and methacrylate basedspreading modifiers may be advantageous because they are generallycompatible with the polyethylene glycol dimethacrylate and acrylate ormethacrylate based multifunctional crosslinking agents of the inkcompositions. As such, their use will not cause the precipitation of theother acrylate or methacrylate based components from solution. Inaddition, acrylate and methacrylate based spreading modifiers canparticipate in the crosslinking of the polyethylene glycoldimethacrylate. That is, the spreading modifier(s) can be incorporatedinto the polymer through similar chemistry, so as not to remain ascontaminants after UV curing. Various embodiments of organic thin layerink compositions comprise the spreading modifiers in amounts of up toabout 15 wt. %. This includes embodiments of the organic thin layer inkcompositions that comprise the spreading modifiers in amounts in therange from about 1 to about 15 wt. %.

In some embodiments of the ink compositions, the spreading modifiercomprises an alkoxylated aliphatic diacrylate. The formula for analkoxylated aliphatic diacrylate can be represented as follows:

where n can be between 3 to 12.

As various embodiments of organic thin layer ink compositions canutilize various alkoxylated aliphatic diacrylate materials for adjustingthe spreading properties of an ink formulation on a substrate, variousembodiments of organic thin layer ink compositions of the presentteachings can have up to about 15 wt. % of an alkoxylated aliphaticdiacrylate component in a formulation. Various alkoxylated aliphaticdiacrylate materials can be provided by Sartomer Corporation. Forexample, examples of candidate Sartomer products can include Sartomerproduct number SR-238B, which is 1,6 hexanediol diacrylate with asurface tension of about 35 at 22° C., as well as Sartomer productnumber SR-9209A, which is described as a proprietary alkoxylatedaliphatic diacrylate and has a surface tension of about 35 dynes/cm at22° C. and a viscosity of about 15 cps at 22° C. For various embodimentsof organic thin layer ink compositions, the aliphatic portion of analkoxylated aliphatic diacrylate component can be between 3 to 12repeating methylene units. For various embodiments of organic thin layerink compositions, the aliphatic portion of an alkoxylated aliphaticdiacrylate component can be between 4 to 6 repeating methylene units.

In addition to various alkoxylated aliphatic diacrylate components,various embodiments of organic thin layer ink compositions can usealkoxylated aliphatic dimethacrylate components to adjust the spreadingcharacteristics of various formulations. Various embodiments of organicthin layer ink compositions of the present teachings can have up toabout 15 wt. % of an alkoxylated aliphatic dimethacrylate component in aformulation. For various embodiments of organic thin layer inkcompositions, the aliphatic portion of an alkoxylated aliphaticdimethacrylate component can be between 3 to 12 repeating methyleneunits. For various embodiments of organic thin layer ink compositions,the aliphatic portion of an alkoxylated aliphatic dimethacrylatecomponent can be between 4 to 6 repeating methylene units. The formulafor an alkoxylated aliphatic dimethacrylate can be represented asfollows:

where n can be between 3 to 12.

Regarding initiation of the polymerization process, various embodimentsof organic thin layer ink compositions of the present teachings canutilize numerous types of photoinitiators for initiating thepolymerization process. In various embodiments the photoinitiators arepresent in amounts in the range from about 0.1 to about 8 wt. %. Thisincludes embodiments in which the photoinitiators are present in amountsin the range from about 1 to about 5 wt. %. However, amounts outside ofthese ranges can also be used. The photoinitiator may be a Type I or aType II photoinitiator. Type I photoinitiators undergo radiation-inducedcleavage to generate two free radicals, one of which is reactive andinitiates polymerization. Type II photoinitiators undergo aradiation-induced conversion into an excited triplet state. Themolecules in the excited triplet state then react with molecules in theground state to produce polymerization initiating radicals.

The specific photoinitiator used for a given ink composition isdesirably selected such that they are activated at wavelengths that arenot damaging to the OLED materials. For this reason, various embodimentsof the ink compositions include photointiators that have a primaryabsorbance with a peak in the range from about 368 to about 380 nm. Thelight source used to activate the photoinitiators and induce the curingof the ink compositions is desirably selected such that the absorbancerange of the photoinitiator matches or overlaps with the output of thelight source, whereby absorption of the light creates free radicals thatinitiate polymerization. Suitable light sources may include mercury arclamps and UV light emitting diodes.

An acylphosphine oxide photoinitiator can be used, though it is to beunderstood that a wide variety of photoinitiators can be used. Forexample, but not limited by, photoinitiators from the α-hydroxyketone,phenylglyoxylate, and α-aminoketone classes of photoinitiators can alsobe considered. For initiating a free-radical based polymerization,various classes of photoinitiators can have an absorption profile ofbetween about 200 nm to about 400 nm. For various embodiments of thecompositions and methods disclosed herein,2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO) and2,4,6-trimethylbenzoyl-diphenyl phosphinate have desirable properties.For various embodiments of the compositions and methods of the presentteaching, an acylphosphine oxide photoinitiator can be about 0.1-5 wt. %of a formulation. Examples of acylphosphine photoinitiators includeIrgacure® TPO initiators for UV curing sold under the tradenamesIrgacure® TPO, a type I hemolytic initiator which; with absorption @ 380nm; Irgacure® TPO-L, a type I photoinitiator that absorbs at 380 nm; andIrgacure® 819 with absorption at 370 nm. By way of illustration, a lightsource emitting at a nominal wavelength in the range from 350 nm to 395nm at a radiant energy density of up to 1.5 J/cm² could be used to curean ink composition comprising a TPO photoinitiator. Using theappropriate energy sources, high levels of curing can be achieved. Forexample, some embodiments of the cured films have a degree of curing of90% or greater, as measured by Fourier Transform Infrared (FTIR)spectroscopy.

The appropriate amount of photoinitiator to include in a given inkcomposition will depend on the nature of the selected photoinitiator,crosslinking agent and, if present, spreading modifier. However, theamount of photoinitiator is desirably selected to minimize the volumechange that takes place from the time the ink composition is printed tothe time the ink composition is cured into a solid film. For example,for some embodiments of the ink compositions, the volume differencebetween the layer of printed ink composition and the solid organicpolymeric thin film formed via curing the ink composition is no greaterthan 1%. Minimizing the volume change that occurs during curing improvesthe uniformity of the cured film.

The present inventors have developed an accurate test for measuring thevolume change of ink compositions that takes place during the curing.This test allows for the precise determination of the appropriate amountof photoinitiator to be included in a given ink composition formulationin order to minimize the volume change that results from curing. In thetest, a known volume of an ink composition is carefully dispensed intothe bottom of a container with a known volume marking (for example, avolumetric flask). The ink composition in the container is then exposedto a radiation source that induces crosslinking and cures the inkcomposition into a solid film. A volume of deionized (DI) watercorresponding to the volume indicated by the volume marking on thecontainer is then dispensed into the container with the cured film. Theportion of the DI water above the volume marking is then extracted fromthe container and weighed to determine the volume of the cured film. Byway of illustration, the test can be carried out in a laboratory asfollows. Place a 5 mL glass volumetric flask into a glove box, alongwith a UV-curable ink composition, and a hand-held ultraviolet (UV)lamp. Using an Eppendorf pipette and an appropriate tip, carefullydispense 500 μL of the ink composition into the volumetric flask withouttouching the tip to the side walls, such that all of the ink compositionis dispensed into the bottom of flask. Place the volumetric flask overthe UV lamp and turn on the lamp to an appropriate wavelength setting(e.g., 365 nm) for a time sufficient to fully cure the ink composition(e.g., about 180 seconds). Note: the operator should be wearing UVprotective glasses. After the ink composition has cured into a solidfilm, turn off the lamp and place a stopper on flask. Take the stopperedflask with the cured film out of the glove box. Place the flask on aweighing balance, without the glass stopper, and measure its tareweight. Using a Pasteur pipette, carefully dispense (avoiding the sidewalls) precisely 5 grams of DI water into the volumetric flask. Thenremove the flask from the balance, place an empty dry vial on thebalance and measure its tare weight. Using a fresh dry Pasteur pipettecarefully extract the portion of DI water from volumetric flask that isabove the 5 mL mark. At the endpoint of the extraction, the low point ofthe meniscus of the water must be aligned with the 5 mL mark, asdetermined by visual inspection. Transfer the full amount of theextracted DI water into the empty vial and measure its weight (w1). Thepercent volume change (e.g., volume reduction) resulting from the curingof the dispensed ink composition can be calculated using the followingequation:

Volume change %=100−((w1grams/0.5grams)×100).

Using this test method, it has been discovered that even small changesin the amount of photoinitiator in the ink compositions can have asubstantial affect on volume change that takes place during curing andthat this test can be used to formulate ink compositions that undergovolume changes during curing of no greater than 1%. Various embodimentsof the ink composition undergo volume changes during curing of nogreater than 0.5%.

By way of illustration, the test method was used to formulate an inkcomposition comprising polyethylene glycol 200 dimethacrylate,pentaerythritol tetraacrylate (PET), SR-9209A and2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO) as aphotoinitiator. Five ink compositions were formulated. Each compositioncontained 4 wt. % SR-9209A and 7 wt. % PET. The amount of TPO wasadjusted as shown in Table 1 and the balance was polyethylene glycol 200dimethacrylate. In each test 0.5 ml of the ink composition was initiallydispensed into the flask. Except where otherwise indicated, the curetime was 180 seconds.

TABLE 1 Volume Changes as a Result of Curing. Weight Post Curing VolumeInk of Extracted Change from Liquid Ink to Composition TPO (wt. %) DIWater (g) Solid Cured Film 1 0.5 0.4471 −11.58% 2 3 0.4891 −2.18% 3 3.50.4928 −1.44% 4 4 0.4977 −0.46% 5 4.5 0.5059 1.18%* 6 ~7.5 0.52144.28%** *Cure time = 300 seconds **Cure time = 420 secondsAs shown in this table and graphically in FIG. 12, a quantity of 4 wt. %TPO provided the lowest volume change. The volume increases for samples5 and 6 were the result of film swelling. The weight loss of the curedfilms was also measured via thermogravimetric analysis for the inkcompositions having different TPO concentrations. The results, which arepresented in Table 2 and graphically in FIG. 13, show that aconcentration of 4 wt. % TPO also resulted in the lowest weight loss.

TABLE 2 TGA Analysis of Cured Films with Different % of Photoinitiator.Post Curing Weight Loss from Liquid Ink to Solid Cured Film at InkComposition TPO (wt. %) 120° C. (wt. %) 1 0.5 1.9 2 3 0.8 4 4 0.5 5 4.51.2

Generally, for ink compositions useful for inkjet printing applications,the surface tension, viscosity and wetting properties of the inkcompositions should be tailored to allow the compositions to bedispensed through an inkjet printing nozzle without drying onto orclogging the nozzle at the temperature used for printing (e.g., roomtemperature; ˜22° C.). Once formulated, various embodiments of organicthin layer ink compositions can have a viscosity of between about 10 andabout 25 (including, for example, between about 17 and about 21)centipoise at 22° C. and a surface tension of between about 32 and about45 (including, for example, between about 38 and about 41) dynes/cm at22° C. As jetting temperatures can be between about 22° C. to about 40°C., over such a temperature range, various embodiments of organic thinlayer ink formulations can have a viscosity of between about 7-25(including, for example, between about 9 and about 19) centipoise and asurface tension of between about 30 and about 45 dynes/cm in thetemperature range of the printhead.

Given that the initiation of polymerization can be induced by light,inks can be prepared to prevent exposure to light. With respect topreparation of organic thin layer ink compositions of the presentteachings, in order to ensure the stability of various compositions, thecompositions can be prepared in a dark or very dimly lit room. Forexample, for the preparation of 30 grams of an embodiments of an organicthin film ink formulation, in a fashion that protects the directexposure to light, the lid of a clean 40 mL amber vial (for example,Flacons, VWR trace clean) can be removed and then can be placed on abalance; and tared. First, a desired amount of a photoinitiator can beweighed into the vial. For example, 1.2 gram of2,4,6-trimethylbenzoyl-diphenylphosphine oxide can be weighed into thevial for a target 4 wt. % of a 30 gram formulation. Next, 1.2 grams ofSR-9209A can be weighed into the vial for a target of 4 wt. %. After theaddition of the alkoxylated aliphatic diacrylate component, 25.5 gramsof polyethylene glycol 200 dimethacrylate can be weighed into the vial,representing 85% of the 30 gram formulation. The final 7% of thecomposition can be provided by weighing 2.1 grams of pentaerythritoltetraacrylate into the vial. Regarding mixing to provide uniformconcentration of components, carefully insert a Teflon® coated magneticstir bar into the vial and secure the cap of vial. Stir the solution for30 minutes at temperatures in the range from room temperature to 50° C.and 600-1000 rpm. Thereafter, filter the ink solution through 0.2 or0.45 μm PTFE syringe filter or vacuum or pressure filtration methods,and sonicate the filtered solution for 30 minutes at ambienttemperature. The ink composition is ready for use and should be storedaway from light in an inert environment, for example, in a glove box.Various embodiments of an organic thin film ink preparation as describedcan have a viscosity of between about 17 and about 19 centipoise at 22°C. and a surface tension of between about 37 and about 41 dynes/cm at22° C.

Once the ink compositions are prepared, they can be dehydrated by mixingin the presence of molecular sieve beads for a period of a day or moreand then stored under a dry, inert atmosphere, such as a compressed dryair or nitrogen atmosphere. The ink composition should be stored inamber light or in the dark in order to avoid or minimize prematurepolymerization. For example, the ink composition can be stored in anamber vial.) Drying and storage in a dry, inert atmosphere can keep thewater content of the ink compositions below about 300 ppm (including,for example, below about 200 ppm), which is desirable for ink jetprinting, until the compositions are ready for use. Using the inkcomposition prepared as described above, a dehydration process wascarried out and evaluated as follows. First a 2 gram aliquot of the inkcomposition (prior to drying) was removed and its H₂O content wasdetermined to be about 1200 ppm using Karl Fischer coulometrictitration. To the remainder of the ink composition was added 3 Angstrommolecular sieve beads (10% w/w). The composition was then placed on aroller to provide gentle agitation for 5 days, after which the inkcomposition was transferred into the glove box (H₂O<10 ppm) andaliquoted into 20 amber vials (2 mL each), followed by capping thevials, to provide a nitrogen headspace in the vials. The remainder ofthe ink composition was removed from the glove box and aliquoted, underambient environment, into 20 amber vials (2 mL each), followed bycapping the vials. The glove box aliquoted vials were removed from theglove box (under an N₂ headspace) and, along with the vials aliquotedoutside the glove box (under ambient headspace), stowed under a fumehood. Thereafter, one vial (each) was opened from the N₂ headspace groupand the ambient headspace group and the water contents of the inkcompositions were measured, using Karl Fischer coulometric titration,from day 0 through 4 (daily) and then on a weekly/biweekly basis up today 51. The data showed that the ink compositions maintained under anitrogen atmosphere (headspace) had a water content of only 120 ppmafter 51 days, while the ink compositions maintained under an ambientatmosphere had a water content that was three times as high (361.2 ppm)on day 51. The same procedure can be used to produce the same resultswith a compressed dry air headspace.

The ink compositions, particularly those stored under a dry, inertatmosphere at room temperature (22° C.), can be stable for long periodsof time, as determined by the lack of precipitation or separation undervisual inspection and the stabilities in their room temperatureviscosities and surface tensions. Some embodiments of ink compositionsexperience a surface tension change of 2% or less (for example, 1% orless) and a viscosity change of 6% or less over a period of at least 160days at room temperature under a compressed dry air or under a nitrogenatmosphere in the dark. For example, the viscosity (measured with aBrookfield viscometer) of the ink composition prepared, dehydrated andstored under compressed dry air or under a nitrogen atmosphere in thedark, as described above, increased from 17.8 cP to only 18.7 cP over aperiod of 160 days at room temperature. At least a portion of this minorincrease may be attributed to the limits of reproducibility of theinstrument. The surface tension (measured via dynamic SITA) of the inkcomposition changed from 39.9 dyne/cm² to 39.7 dyne/cm²—a statisticallyinsignificant amount—over the same period.

An embodiment of an ink prepared as described above was formulated andprinted using a printing system as described in U.S. Pat. No. 8,714,719,which is incorporated herein in its entirety. The films were cured in aninert nitrogen environment using UV radiation. The cured films displayedhigh transparency, as well as being of uniform thickness. By way ofillustration, some embodiments of cured films made with the present inkcompositions have a film thickness variation of 5% or lower. Filmthickness uniformity can be measured using a profilometer tool, such asa Veeco Dektak Profilometer tool. To carry out a thickness measurement,a scratch can be made on the film using, for example, a sharp needle ona substrate. Then the substrate can be placed on the tool to measure theheight of the scratch well, which represents the thickness of the filmprinted on the substrate. FIG. 2A displays a film of 8 μm thickness,which was printed without incorporating edge compensation, and showsuniformity except at the film edges, as expected. FIG. 2B is a film of16 μm thickness, which was printed using edge compensation, and showsuniformity, as expected. Further by way of illustration, someembodiments of the cured films made with the present ink compositionshave a transmission of 90% or greater at wavelengths of 550 nm andabove. This includes cured films having a transmission of 99% orgreater, and 99.5% or greater, at wavelengths of 550 nm and above.

The suitability of an ink composition for inkjet printing applicationscan be measured by its maximum stable jetting frequency through a nozzleof an inkjet printhead. An ink composition that displays stable jettinghas constant, or substantially constant, drop velocities, drop volumesand drop trajectories over a range of jetting frequencies. Beyond theink composition's stable jetting frequency range, however, its dropvelocity, drop volume and/or drop trajectory become erratic withincreasing jetting frequency. In order to provide an ink compositionwith a stable jetting frequency, it is desirable to formulate the inkcompositions from components that themselves have good jettingproperties. Thus, in some embodiments of the ink compositions thespreading modifier is selected such that it is characterized by a highjetting stability. Various embodiments of the present ink compositionscomprise spreading modifiers with maximum stable jetting frequencies ofat least 23 kHz at 22° C. This includes embodiments of the inkcompositions that comprise spreading modifiers having maximum stablejetting frequencies of at least 24 kHz at 22° C. and further includesembodiments of the ink compositions that comprise spreading modifiershaving maximum stable jetting frequencies of at least 25 kHz at 22° C.

Stable jetting through an inkjet nozzle is illustrated in FIGS. 9(A),9(B) and 9(C), which show the effect of increased jetting frequency ondrop volume, drop velocity and drop trajectory (angle), respectively,for the spreading modifier SR-9209A that displays stable jetting up to ajetting frequency of about 24 kHz at 22° C. and up to about 26 kHz at25° C. The frequency responses shown in FIGS. 9(A) through 9(C) weremeasured by loading the SR-9209A into a printhead that is coupled with adrop measuring instrument. A waveform for firing is developed and thepulse times and voltages are adjusted and optimized to establish astable jetting range. For example, ink jet tests can be conducted toassess the print performance of a spreading modifier by examining theeffects of changing the frequency on drop volume, drop velocity and droptrajectory at 22° C. and 25° C. Examples of results from this type offrequency response test, after optimizing the pulse times and voltages,are illustrated in the graphs of FIG. 9(A) through 9(C), which show thefrequency response of drop volume, velocity and trajectory respectively,for the SR-9209A. The tests were run using a Dimatix™ SX3 printhead anda JetXpert shadowgraphy setup by ImageXpert® as a drop measuringinstrument.

The jetting frequency response of a given composition, such as aspreading modifier, may display some undulating variation in drop volumeand drop velocity as the jetting frequency increases, but prior to theonset of the erratic jetting frequency response that characterizesunstable jetting. It is desirable for a composition to minimize theextent of these drop volume and velocity variations in order to provideuniform and reproducible deposition even at the higher frequency end ofthe composition's stable jetting frequency range. Various embodiments ofthe present ink compositions comprise spreading modifiers that undergodrop volume variations of no more than about 15% up to their maximumstable jetting frequency at 22° C. This includes ink compositions thatcomprise spreading modifiers that undergo drop volume variations of nomore than about 12% up to their maximum stable jetting frequency at 22°C. and further includes ink compositions that comprise spreadingmodifiers that undergo drop volume variations of no more than about 10%up to their maximum stable jetting frequency at 22° C. Variousembodiments of the present ink compositions comprise spreading modifiersthat undergo drop velocity variations of no more than about 15% up totheir maximum stable jetting frequency at 22° C. This includes inkcompositions that comprise spreading modifiers that undergo dropvelocity variations of no more than about 12% up to their maximum stablejetting frequency at 22° C. and further includes ink compositions thatcomprise spreading modifiers that undergo drop velocity variations of nomore than about 10% up to their maximum stable jetting frequency at 22°C.

Drop volume and velocity variations as a function of jetting frequencyat 22° C. and 25° C. are illustrated in FIGS. 10(A) and 10(B), whichshow the drop volume and drop velocity variations, respectively, for theSR-9209A of FIGS. 9(A)-9(C). The SR-9209A has a drop volume variation ofno greater than about 10% and a drop velocity variation of no greaterthan about 12% up to the maximum stable jetting frequency at 25° C.

The formulated ink compositions comprising the spreading modifiers arealso capable of stable jetting at high frequencies at room temperatureand even higher jetting temperatures, including jetting temperatures ofup to about 50° C. By way of illustration, an ink composition containing4 wt. % SR-9209A, 7 wt. % PET, 4 wt. % TPO and 85 wt. % polyethyleneglycol 200 dimethacrylate was jetted using the procedure described abovefor jetting the spreading modifier SR-9209A. This procedure used aprinthead and a drop measuring instrument similar to those used in theabove-described jetting frequency response tests for the spreadingmodifier. The printer used in the testing had four rows per printheadand 28 nozzles per row. The results for the drop velocity, volume andtrajectory are shown in FIGS. 11(A), 11(B) and 11(C), respectively. Thetraces in FIGS. 11(A)-11(C) show the mean values for the 28 nozzles foreach of the four printhead rows. As illustrated in these figures, stablejetting was observed for the ink composition at 25° C. for jettingfrequencies up to at least 25 kHz. The tests were repeating for the inkcomposition at a jetting temperature of 40° C. and, again, stablejetting in terms of drop velocity, volume and trajectory was observedfor jetting frequencies up to at least 25 kHz.

Systems and Methods for Organic Thin Film Formation on a Substrate

As previously discussed herein, manufacture of various OLED devices on avariety of substrates can be done in an inert, substantiallyparticle-free environment to ensure high-yield manufacturing.

For clearer perspective regarding substrate sizes that can be used inmanufacturing of various OLED devises, generations of mother glasssubstrate sizes have been undergoing evolution for flat panel displaysfabricated by other-than OLED printing since about the early 1990's. Thefirst generation of mother glass substrates, designated as Gen 1, isapproximately 30 cm×40 cm, and therefore could produce a 15″ panel.Around the mid-1990's, the existing technology for producing flat paneldisplays had evolved to a mother glass substrate size of Gen 3.5, whichhas dimensions of about 60 cm×72 cm. In comparison, a Gen 5.5 substratehas dimensions of about 130 cm×150 cm.

As generations have advanced, mother glass sizes for Gen 7.5 and Gen 8.5are in production for other-than OLED printing fabrication processes. AGen 7.5 mother glass has dimensions of about 195 cm×225 cm, and can becut into eight 42″ or six 47″ flat panels per substrate. The motherglass used in Gen 8.5 is approximately 220×250 cm, and can be cut to six55″ or eight 46″ flat panels per substrate. The promise of OLED flatpanel display for qualities such as truer color, higher contrast,thinness, flexibility, transparency, and energy efficiency have beenrealized, at the same time that OLED manufacturing is practicallylimited to G 3.5 and smaller. Currently, OLED printing is believed to bethe optimal manufacturing technology to break this limitation and enableOLED panel manufacturing for not only mother glass sizes of Gen 3.5 andsmaller, but at the largest mother glass sizes, such as Gen 5.5, Gen7.5, and Gen 8.5. One of the features of OLED panel display technologyincludes that a variety of substrate materials can be used, for example,but not limited by, a variety of glass substrate materials, as well as avariety of polymeric substrate materials. In that regard, sizes recitedfrom the terminology arising from the use of glass-based substrates canbe applied to substrates of any material suitable for use in OLEDprinting.

Table 2 below relates generation substrate designation to sizes as oftencan be found in various sources relating to generation substrates forvarious OLED devices. Table 3 below summarizes aspect ratios and areasfor some known generation-sized substrates as currently available invarious sources relating to generation-sized substrates. It should beunderstood that variation of aspect ratio and hence size may be seenfrom manufacturer to manufacturer. Additionally, It should be theinformation provided in Table 3 can be subject to change, given theevolution of the industry. In that regard, updated conversion factorsfor a specific generation-sized substrate, as well as area in squaremeters can be obtained any of a variety of generation-sized substrates.

TABLE 2 Correlation between area and substrate size Generation ID X (mm)Y (mm) Area (m²) Gen 3.0 550 650 0.36 Gen 3.5 610 720 0.44 Gen 3.5 620750 0.47 Gen 4 680 880 0.60 Gen 4 730 920 0.67 Gen 5 1100 1250 1.38 Gen5 1100 1300 1.43 Gen 5.5 1300 1500 1.95 Gen 6 1500 1850 2.78 Gen 7.51950 2250 4.39 Gen 8 2160 2400 5.18 Gen 8 2160 2460 5.31 Gen 8.5 22002500 5.50 Gen 9 2400 2800 6.72 Gen 10 2850 3050 8.69

Manufacturing tools that in principle can allow for the printing of avariety of substrate sizes that includes large-format substrate sizes,can require substantially large facilities for housing such OLEDmanufacturing tools. Accordingly, maintaining an entire large facilityunder an inert atmosphere presents engineering challenges, such ascontinual purification of a large volume of an inert gas. Variousembodiments of a gas enclosure system can have a circulation andfiltration system internal a gas enclosure assembly in conjunction witha gas purification system external a gas enclosure that together canprovide continuous circulation of a substantially low-particulate inertgas having substantially low levels of reactive species throughout a gasenclosure system. According to the present teachings, an inert gas maybe any gas that does not adversely alter a product being fabricatedunder a defined set of conditions. Some commonly used non-limitingexamples of an inert gas for the processing of various embodiments of anOLED device can include nitrogen, any of the noble gases, and anycombination thereof. Systems and methods of the present teachings canprovide a large facility that is essentially hermetically sealed toprevent contamination of various reactive atmospheric gases, such aswater vapor and oxygen, as well as organic solvent vapors generated fromvarious printing processes. According to the present teachings, an OLEDprinting facility would maintain levels for each species of variousreactive species, including various reactive atmospheric gases, such aswater vapor and oxygen, as well as organic solvent vapors at 100 ppm orlower, for example, at 10 ppm or lower, at 1.0 ppm or lower, or at 0.1ppm or lower.

The need for printing an OLED panel in a facility in which the levels ofeach of a reactive species should be maintained at targeted low levelscan be illustrated in reviewing the information summarized in Table 4.The data summarized on Table 4 resulted from the testing of each of atest coupon comprising organic thin film compositions for each of red,green, and blue, fabricated in a large-pixel, spin-coated device format.Such test coupons are substantially easier to fabricate and test for thepurpose of rapid evaluation of various formulations and processes.Though test coupon testing should not be confused with lifetime testingof a printed panel, it can be indicative of the impact of variousformulations and processes on lifetime. The results shown in the tablebelow represent variation in the process step in the fabrication of testcoupons in which only the spin-coating environment varied for testcoupons fabricated in a nitrogen environment where reactive species wereless than 1 ppm compared to test coupons similarly fabricated but in airinstead of a nitrogen environment.

It is evident through the inspection of the data in Table 4, shownbelow, for test coupons fabricated under different processingenvironments, particularly in the case of red and blue, that printing inan environment that effectively reduces exposure of organic thin filmcompositions to reactive species may have a substantial impact on thestability of various ELs, and hence on lifetime. The lifetimespecification is of particular significance for OLED panel technology,as this correlates directly to display product longevity; a productspecification for all panel technologies, which has been challenging forOLED panel technology to meet. In order to provide panels meetingrequisite lifetime specifications, levels of each of a reactive species,such as water vapor, oxygen, as well as organic solvent vapors, can bemaintained at 100 ppm or lower, for example, at 10 ppm or lower, at 1.0ppm or lower, or at 0.1 ppm or lower with various embodiments of a gasenclosure system of the present teachings.

TABLE 3 Impact of inert gas processing on lifetime for OLED panelsProcess V Cd/A CIE (x, y) T95 T80 T50 Color Environment @ 10 mA/cm² @1000 Cd/m² Red Nitrogen 6 9 (0.61, 0.38) 200 1750 10400 Air 6 8 (0.60,0.39) 30 700 5600 Green Nitrogen 7 66 (0.32, 0.63) 250 3700 32000 Air 761 (0.32, 0.62) 250 2450 19700 Blue Nitrogen 4 5 (0.14, 0.10) 150 7503200 Air 4 5 (0.14, 0.10) 15 250 1800

In addition to providing an inert environment, maintaining asubstantially low-particle environment for OLED printing is ofparticular importance, as even very small particles can lead to avisible defect on an OLED panel. Particle control in a gas enclosuresystem can present significant challenges not presented for processesthat can be done, for example, in atmospheric conditions under open air,high flow laminar flow filtration hoods.

For example, of a manufacturing facility can require a substantiallength of various service bundles that can be operatively connected fromvarious systems and assemblies to provide optical, electrical,mechanical, and fluidic connections required to operate, for example,but not limited by, a printing system. Such service bundles used in theoperation of a printing system and located proximal to a substratepositioned for printing can be an ongoing source of particulate matter.Additionally, components used in a printing system, such as fans orlinear motion systems that use friction bearing, can be particlegenerating components. Various embodiments of a gas circulation andfiltration system of the present teachings can be used in conjunctionwith particle control components to contain and exhaust particulatematter. Additionally, by using a variety of intrinsically low-particlegenerating pneumatically operated components, such as, but not limitedby, substrate floatation tables, air bearings, and pneumaticallyoperated robots, and the like, a low particle environment for variousembodiments of a gas enclosure system can be maintained. Regardingmaintaining a substantially low-particle environment, variousembodiments of a gas circulation and filtration system can be designedto provide a low particle inert gas environment for airborneparticulates meeting the standards of International StandardsOrganization Standard (ISO) 14644-1:1999, “Cleanrooms and associatedcontrolled environments—Part 1: Classification of air cleanliness,” asspecified by Class 1 through Class 5

As depicted in FIG. 3, process 100 for printing an organic thin film inkon a substrate and then curing the ink can include step 110 oftransferring a substrate from a manufacturing tool in which, forexample, an inorganic encapsulation layer was fabricated on an OLEDsubstrate device using a vapor deposition process. As will be discussedin more detail subsequently herein, a substrate can be transferred froman inorganic encapsulation fabrication tool to a printing module of aprinting tool There can be many advantages of inkjet printing for avariety of processes that can utilize pattered area printing. First, arange of vacuum processing operations can be eliminated because suchinkjet-based fabrication can be performed at atmospheric pressure.Additionally, during an inkjet printing process, an organicencapsulation layer can be localized to cover portions of an OLEDsubstrate over and proximal to an active region, to effectivelyencapsulate an active region, including lateral edges of the activeregion. The targeted patterning using inkjet printing results ineliminating material waste, as well as eliminating additional processingtypically required to achieve patterning of an organic layer, which canresult in enhanced particle contamination. For example, masking is awell-known technique used for patterned film deposition, however,masking techniques can create substantial particle contamination.

In step 120, using various embodiments of organic thin layer inksaccording to the present teachings, a printing tool can be used to printan organic thin film layer over a target print area. In the art ofprocessing, total average cycle time or TACT can be an expression of aunit of time for a particular process cycle. For various embodiments ofsystems and methods of the present teachings, for a step of printing anorganic thin film ink, TACT can be between about 30 seconds to about 120seconds. Subsequently, as indicated by step 130, the substrate can betransferred from a printing module of a printing tool to a curingmodule. With respect to a step of curing, as indicated by step 140,according to various embodiments of systems and methods of the presentteachings, before curing is initiated, a step of allowing the printedorganic thin film ink to reach a film layer of uniform thickness can bedone. In various embodiments, such a leveling step can be considered aseparate step. In various embodiments of systems and methods, levelingcan be done in a dedicated chamber, for example, in a holding chamber,and then a substrate can be transferred to a curing chamber. For variousembodiments of the present teachings, as will be discussed in moredetail herein, a step of leveling can be done in the same chamber as thestep of curing. According to various embodiments of systems and methodsof the present teachings, TACT for a step of leveling can be betweenabout 170 seconds to about 210 seconds, while TACT for a curing stepaccording to some embodiments can be between about 15 seconds to 60seconds, while for other embodiments can be between about 25 seconds toabout 35 seconds. After curing step 140, a substrate can be transferredfrom a UV curing module to another processing chamber, such as an outputloadlock chamber, as indicated by process step 150 of process 100.

In order to accomplish process 100 of FIG. 3, various embodiments ofmanufacturing tools of the present teachings that can provide inert,substantially particle-free environments can be used, for example, asshown in FIG. 4. FIG. 4 depicts a perspective view of OLED printing tool4000 according to various embodiments of the present teachings, whichcan include first module 4400, printing module 4500, and second module4600. Various modules, such as first module 4400 can have first transferchamber 4410, which can have a gate, such as gate 4412, for each side offirst transfer chamber 4410 to accommodate various chambers having aspecified function. As depicted in FIG. 4 first transfer chamber 4410can have a load lock gate (not shown) for integration of first load lockchamber 4450 with first transfer chamber 4410, as well as a buffer gate(not shown) for integration of first buffer chamber 4460 with firsttransfer chamber 4410. Gate 4412 of first transfer chamber 4410 can beused for a chamber or unit that can be movable, such as, but not limitedby, a load lock chamber. Observation windows, such as observationwindows 4402 and 4404 of first transfer chamber 4410, as well asobservation window 4406 of first buffer chamber 4460, can be providedfor an end user to, for example, monitor a process. Printing module 4500can include gas enclosure 4510, which can have first panel assembly4520, printing system enclosure assembly 4540, and second panel assembly4560. Gas enclosure 4510 can house various embodiments of a printingsystem.

Various embodiments of a gas enclosure can be contoured around aprinting system base, upon which a substrate support apparatus can bemounted. Further, a gas enclosure can be contoured around a bridgestructure used for the X-axis movement of a carriage assembly. As anon-limiting example, various embodiments of a contoured gas enclosureaccording to the present teachings can have a gas enclosure volume ofbetween about 6 m³ to about 95 m³ for housing various embodiments of aprinting system capable of printing substrate sizes from Gen 3.5 to Gen10. By way a further non-limiting example, various embodiments of acontoured gas enclosure according to the present teachings can have agas enclosure volume of between about 15 m³ to about 30 m³ for housingvarious embodiments of a printing system capable of printing, forexample, Gen 5.5 to Gen 8.5 substrate sizes. Such embodiments of acontoured gas enclosure can be between about 30% to about 70% savings involume in comparison to a non-contoured enclosure having non-contoureddimensions for width, length and height.

Second module 4600 of FIG. 4 can include second transfer chamber 4610,which can have a gate, such as gate 4612, for each side of secondtransfer chamber 4610 to accommodate various chambers having a specifiedfunction. As depicted in FIG. 4 second transfer chamber 4610 can have aload lock gate (not shown) for integration of second load lock chamber4650 with second transfer chamber 4610, as well as a gate (not shown)for integration of second chamber 4660 with second transfer chamber4610. Gate 4612 of second transfer chamber 4610 can be used for achamber or unit that can be movable, such as, but not limited by, a loadlock chamber. Observation windows, such as observation windows 4602 and4604 of second transfer chamber 4610, can be provided for an end userto, for example, monitor a process. According to various embodiments ofsystems and methods of the present teachings, chamber 4660 of FIG. 4 canbe a UV curing module. For example, chamber 4660 of FIG. 4 can be a UVcuring module as depicted in FIG. 5.

First load lock chamber 4450 and second load lock chamber 4650 can beaffixably associated with first transfer chamber 4410 and secondtransfer chamber 4610, respectively or can be movable, such as on wheelsor on a track assembly, so that they can be readily positioned for useproximal a chamber. According to the present teachings, a load lockchamber can be mounted to a support structure and can have at least twogates. For example first load lock chamber 4450 can be supported byfirst support structure 4454 and can have first gate 4452, as well as asecond gate (not shown) that can allow fluid communication with firsttransfer module 4410. Similarly, second load lock chamber 4650 can besupported by second support structure 4654 and can have second gate4652, as well as a first gate (not shown) that can allow fluidcommunication with second transfer module 4610.

FIG. 5 illustrates generally an example an ultraviolet (UV curing)module that can be used in manufacturing a light emitting device. Thetreatment system can be included as a portion of other systems ortechniques described herein. For example, as indicated in FIG. 5, UVcuring module 4660 could be chamber 4660 of OLED printing tool 4000 ofFIG. 4. The system can include various regions, such as for use as acuring chamber, or for use as a combination curing and holding chamber.For various embodiments of a curing chamber, a source of ultravioletemission can be used such as to treat one or more layers deposited on asubstrate being fabricated. For example, ultraviolet emission can beused to polymerize or otherwise treat an organic layer deposited on thesubstrate, such as for use in one or more processes related tomanufacturing a flat panel display assembly, such as including an OLEDdisplay assembly.

According to the present teachings, a UV curing module can include oneor more enclosed UV curing chambers such as first UV curing chamber4661A, second UV curing chamber 4661B, and “Nth” UV curing chamber4661N. For example, three regions can be included and in anotherexample, other numbers of regions can be included. The regions can beoriented in a “stacked” configuration along a vertical axis of thesystem, such as shown illustratively in FIG. 5. Other configurations canbe used, such as a radial configuration of chambers extending outwardfrom a central chamber. For example, transfer chamber 4610 of FIG. 5 canbe second transfer chamber 4610 of FIG. 4.

In an illustrative example, such as after deposition of an organic layeron a substrate, a leveling operation can be performed. As was previouslydiscussed herein, a duration of a leveling operation can generally begreater than a duration of an ultraviolet treatment operation.Accordingly, in one approach, respective holding regions or “buffercells” can be used, such as in a stacked configuration with each regionconfigured to house a substrate. In this approach, the levelingoperation can proceed without restricting access or otherwise tying up aseparate ultraviolet treatment region. However, multiple ultravioletsources can be used, such including user lower-cost sources. In thismanner, a throughput impact of idling an ultraviolet source need notpreclude use of the same UV curing chamber (e.g., 4661A through 4661N)for both a holding operation (e.g., buffering or leveling), as well asfor an ultraviolet treatment operation, because multiple regions can beconfigured to provide ultraviolet treatment. Such an approach can alsoprovide redundancy of the ultraviolet sources such that processing cancontinue even if a particular ultraviolet source fails or is undergoingmaintenance.

For example, first radiation source 4662A (e.g., an ultraviolet-emittingLED array) can provide ultraviolet emission, depicted as multiple arrowsin FIG. 5. A UV apparatus can include a UV single source, a liner array,or a two dimensional array of UV source. The type of source selected canhave a specified range of wavelengths to a first substrate 2050A. Asdepicted in FIG. 5, a first set of radiation sources 4662A are depicted.Though the term “UV” is used, it is to be understood that the source hasa wavelength of light associated with an energy required to initiate apolymerization reaction. In that regard, as free-radical initiation canoccur via thermal decomposition as well as photolysis, a source ofradiation can include any source effective in initiating apolymerization reaction through a variety of mechanism. Theelectromagnetic radiation emission can be coupled to an interior of theenclosed region of first UV chamber 4661A such as through a window 4663(e.g., a quartz window or an assembly such as including a normalizationfilter, or other filters or coatings). According to various embodimentsof the present teachings, the environment within UV curing chamber 4661Acan be inert and can be isolated from a housing containing the first setof radiation sources 4662A. According to various systems and methods, inthe second enclosed region of UV chamber 4661B, for example, the secondsubstrate 2050B can be held for a specified duration, such as forleveling or to await availability of other processes. During thespecified holding duration, a second set of radiation sources 4662B canbe disabled.

Regarding support of substrates, such as 2050A and 2050B of FIG. 5, thepresent inventors have recognized, among other things, that for someoperations or material systems, such as in relation to leveling adeposited organic layer, visible defects can be induced in the displayregions of a substrate when the substrate is supported in a non-uniformmanner. For example, pins, support frames, retracted lift-pins, orvacuum apertures in contact with a substrate can induce visible defectsin a finished device.

Without being bound by theory, it is believed that such defectsprimarily result from localized variations in thermal conductivity thatcan create local gradients in the temperature of a substrate during, forexample, a leveling operation. In an example, a specified temperatureuniformity can be maintained in a local region of the substrate, forexample, such that deviation in temperature adjacent to or within thelocal region is limited. For example, a significant temperaturevariation across the substrate can be tolerated but such variation canhave a limited gradient such that the temperature does not varysignificantly over a small distance along the substrate. In this manner,abrupt changes in visible characteristics of the finished display can beavoided and such gradual changes are less likely to be noticed or evendetectable.

In one approach, regions outside the emitting or display region of thesubstrate can be used to support a substrate outside of active deviceareas of a substrate. However, because large portions of a substrate caninclude emitting regions or portions of the actual display region, itcan be impractical to support the substrate only at the periphery ofsuch regions because such support induces unacceptable mechanical forcesor stresses elsewhere across a substrate, which may either distort orfracture a substrate. Additionally, the present inventors have alsorecognized that a correlation can exist between particle generation anda number of instances or locations of contact between other apparatusesand a substrate.

Accordingly, the present inventors have recognized that a substrate,such as substrates 2050A and 2050B of FIG. 5 can be supported by achuck, for example chuck 4664 of first UV chamber 4661A, such as duringan ultraviolet treatment operation, such as at least in part using apressurized gas “P” to provide a gas cushion. According to variousexamples, a substrate can be supported exclusively by a controlledarrangement of the pressurized gas, “P such as to float the substrate2050A. In another example, substrate 2050A can be mechanically supportedin part, such as at a periphery, by one or more pins (e.g., a pin 4666)or a support frame, and a weight of substrate 2050A can be supported ina central region of substrate 2050A by the pressurized gas, “P.” Inanother approach, substrate 2050A can be supported by a pressurized gas“P” impinging on a first surface of substrate 2050A, and an opposingforce can be provided such as by a mechanical stop 4668 contacting anopposing face of substrate 2050A. Though first UV chamber 4661A is usedfor the purpose of illustration, it is to be understood that theseteachings apply to all UV chambers shown in FIG. 5. Though pressure isshown for the teachings of FIG. 5, as will be discussed in more detailin reference to the floatation table of FIG. 6, a chuck using pressureand vacuum can also be utilized. In such an example where the substrate2050A is supported exclusively by the gas cushion, a combination ofpositive gas pressure and vacuum can be applied through the arrangementof ports. Such a zone having both pressure and vacuum control caneffectively provide a fluidic spring between floatation chuck 4664 andsubstrate 2050A.

Transfer module 4610 of FIG. 5 can be a transfer module as described forsecond transfer module 4610 of FIG. 4. Regarding the floatation of asubstrate, elevating handler 4612, which can be housed in transfermodule 4610, can also utilized substrate floatation during a transferprocess. Elevating handler 4612 can include a table 4614 (or acorresponding end effector) including pressurized gas “P” to support asubstrate at least in part using the pressurized gas. A conveyor, orother apparatus can be used to transport a substrate from, for example,a printing module, such as printing module 4550 of FIG. 4 through gate4616. Such conveyance means can also include such a pressurized gasarrangement, such that a substrate can be conveyed along a path asindicated by the horizontal arrow shown directing substrate 2050N to UVcuring chamber 4661N.

In the illustrative example of FIG. 5, an enclosed transfer module 4610can house the elevating handler 4612 and table 4614. An inertenvironment having specified gas purity and specified particulate levelscan be established within the enclosed transfer module 4610 as discussedextensively in relation to other examples herein. For example, one ormore fan filter units (FFUs) such as a fan filter unit 5202 can becoupled to transfer module 4610. Duct 5201 can provide a return flow ofinert gas to be recirculated using FFU 5202. A gas purification system3130 can be coupled to the enclosed transfer module 4610. While avertical flow orientation is illustrated in FIG. 5, other configurationscan be used, such as a lateral flow configuration. Each of the regions4661A through 4661N can either share one or more gas purification loopsor can each be served by a respective gas purification loop. Similarly,one or more FFUs can be located to provide a laminar airflow parallel toa surface of substrate in each of the regions 4661A through 4661N. Atemperature within the enclosed transfer module 4610 or within otherportions of the system can be controlled as described extensively inother examples herein, such as using a temperature controller 3140. Aswill be described in more detail in the teachings regarding FIG. 8herein, the temperature controller 3140 can be coupled, for examplethrough a heat exchanger, to the FFU 5202 or one or more FFUs elsewhere.

The regions 4661A through 4661N can each include a valve or gate, suchas to isolate the inert environment of each enclose region 4661A through4661N from the transfer module 4610 or from each other. Accordingly,such as during maintenance, a particular region can have its inertenvironment isolated from the rest of the enclosed regions using a valveor gate.

An OLED inkjet printing system, such as OLED printing system 2000 ofFIG. 6, can be housed in a gas enclosure, such as gas enclosure 4510 ofprinting module 4500 of FIG. 4. Various embodiments of a printing systemof FIG. 6, can be comprised of several devices and apparatuses, whichallow the reliable placement of ink drops onto specific locations on asubstrate. Printing requires relative motion between the printheadassembly and the substrate. This can be accomplished with a motionsystem, typically a gantry or split axis XYZ system. Either theprinthead assembly can move over a stationary substrate (gantry style),or both the printhead and substrate can move, in the case of a splitaxis configuration. In another embodiment, a printhead assembly can besubstantially stationary; for example, in the X and Y axes, and thesubstrate can move in the X and Y axes relative to the printheads, withZ axis motion provided either by a substrate support apparatus or by aZ-axis motion system associated with a printhead assembly. As theprintheads move relative to the substrate, droplets of ink are ejectedat the correct time to be deposited in the desired location on asubstrate. A substrate can be inserted and removed from the printerusing a substrate loading and unloading system. Depending on the printerconfiguration, this can be accomplished with a mechanical conveyor, asubstrate floatation table with a conveyance assembly, or a substratetransfer robot with end effector. For various embodiments of systems andmethods of the present teachings, an Y-axis motion system can be basedon an air-bearing gripper system.

An OLED inkjet printing system, such as OLED printing system 2000 ofFIG. 6, can be comprised of several devices and apparatuses, which allowthe reliable placement of ink drops onto specific locations on asubstrate. These devices and apparatuses can include, but are notlimited to, a printhead assembly, ink delivery system, a motion systemfor providing relative motion between a printhead assembly and asubstrate, substrate support apparatus, substrate loading and unloadingsystem, and printhead management system.

A printhead assembly can include at least one inkjet head, with at leastone orifice capable of ejecting droplets of ink at a controlled rate,velocity, and size. The inkjet head is fed by an ink supply system whichprovides ink to the inkjet head. As shown in an expanded view of FIG. 6,OLED inkjet printing system 2000 can have a substrate, such as substrate2050, which can be supported by a substrate support apparatus, such as achuck, for example, but not limited by, a vacuum chuck, a substratefloatation chuck having pressure ports, and a substrate floatation chuckhaving vacuum and pressure ports. In various embodiments of systems andmethods of the present teachings, a substrate support apparatus can be asubstrate floatation table. As will be discussed in more detailsubsequently herein, substrate floatation table 2200 of FIG. 6 can beused for supporting substrate 2050, and in conjunction with a Y-axismotion system, can be part of a substrate conveyance system providingfor the frictionless conveyance of substrate 2050. A Y-axis motionsystem of the present teachings can include first Y-axis track 2351 andsecond Y-axis track 2352, which can include a gripper system (not shown)for holding a substrate. Y-axis motion can be provided by either alinear air bearing or linear mechanical system. Substrate floatationtable 2200 of OLED inkjet printing system 2000 shown in FIG. 6 candefine the travel of substrate 2050 through gas enclosure assembly 1000of FIG. 1A during a printing process.

FIG. 6 illustrates generally an example of substrate floatation table2200 for a printing system 2000 that can include a floating conveyanceof a substrate, which can have a porous medium to provide floatation. Inthe example of FIG. 6, a handler or other conveyance can be used toposition a substrate 2050 in first region 2201 of a substrate floatationtable 2200, such as located on a conveyor. The conveyer can position thesubstrate 2050 at a specified location within the printing system suchas using either mechanical contact (e.g., using an array of pins, atray, or a support frame configuration), or using gas cushion tocontrollably float the substrate 2050 (e.g., an “air bearing” tableconfiguration). A printing region 2202 of the substrate floatation table2200 can be used to controllably deposit one or more layers on thesubstrate 2050 during fabrication. The printing region 2202 can also becoupled to an second region 2203 of the substrate floatation table 2200.The conveyer can extend along the first region 2201, the printing region2202, and the second region 2203 of the substrate floatation table 2200,and the substrate 2050 can be repositioned as desired for variousdeposition tasks, or during a single deposition operation. Thecontrolled environments nearby the first region 2201, the printingregion 2202, and the second region 2203 can be commonly-shared.According to various embodiments of printing system 2000 of FIG. 6,first region 2201 can be an input region, and second region 2203 can bean output region. For various embodiments of printing system 2000 ofFIG. 6, first region 2201 can be both an input and an output region.Further, function referred to in association with regions 2201, 2202,and 2203, such as input, printing, and output for illustration only.Such regions can be used for other processing steps, such as conveyanceof a substrate, or support of a substrate such as during one or more ofholding, drying, or thermal treatment of the substrate in one or moreother modules.

According to the floatation schemes shown in FIG. 6, in an example wherethe substrate 2050 is supported exclusively by the gas cushion, acombination of positive gas pressure and vacuum can be applied throughthe arrangement of ports or using a distributed porous medium. Such azone having both pressure and vacuum control can effectively provide afluidic spring between the conveyor and a substrate. A combination ofpositive pressure and vacuum control can provide a fluidic spring withbidirectional stiffness. The gap that exists between the substrate(e.g., substrate 2050) and a surface can be referred to as the “flyheight,” and such a height can be controlled or otherwise established bycontrolling the positive pressure and vacuum port states. In thismanner, the substrate Z-axis height can be carefully controlled in, forexample, the printing region 2202. In some embodiments, mechanicalretaining techniques, such as pins or a frame, can be used to restrictlateral translation of the substrate while the substrate is supported bythe gas cushion. Such retaining techniques can include using springloaded structures, such as to reduce the instantaneous forces incidentthe sides of the substrate while the substrate is being retained; thiscan be beneficial as a high force impact between a laterally translatingsubstrate and a retaining means can cause substrate chipping or evencatastrophic breakage.

Elsewhere, as illustrated generally in FIG. 6, such as where the flyheight need not be controlled precisely, pressure-only floatation zonescan be provided, such as along the conveyor in the first or secondregions 2201 or 2203, or elsewhere. A “transition” floatation zone canbe provided such as where a ratio of pressure to vacuum nozzlesincreases or decreases gradually. In an illustrative example, there canbe an essentially uniform height between a pressure-vacuum zone, atransition zone, and a pressure only zone, so that within tolerances,the three zones can lie essentially in one plane. A fly height of asubstrate over pressure-only zones elsewhere can be greater than the flyheight of a substrate over a pressure-vacuum zone, such as in order toallow enough height so that a substrate will not collide with afloatation table in the pressure-only zones. In an illustrative example,an OLED panel substrate can have a fly height of between about 150micrometers (μ) to about 300μ above pressure-only zones, and thenbetween about 30μ to about 50μ above a pressure-vacuum zone. In anillustrative example, one or more portions of the substrate floatationtable 2200 or other fabrication apparatus can include an “air bearing”assembly provided by NewWay® Air Bearings (Aston, Pa., United States ofAmerica).

A porous medium can be used to establish a distributed pressurized gascushion for floating conveyance or support of the substrate 2050 duringone or more of printing, buffering, drying, or thermal treatment. Forexample, a porous medium “plate” such as coupled to or included as aportion of a conveyor can provide a “distributed” pressure to supportthe substrate 2050 in a manner similar to the use of individual gasports. The use of a distributed pressurized gas cushion without usinglarge gas port apertures can in some instances further improveuniformity and reduce or minimize the formation of mura or other visibledefects, such as in those instances where the use of relatively largegas ports to create a gas cushion leads to non-uniformity, in spite ofthe use of a gas cushion.

A porous medium can be obtained such as from Nano TEM Co., Ltd.(Niigata, Japan), such as having physical dimensions specified to occupyan entirety of the substrate 2050, or specified regions of the substratesuch as display regions or regions outside display regions. Such aporous medium can include a pore size specified to provide a desiredpressurized gas flow over a specified area, while reducing oreliminating mura or other visible defect formation.

Printing requires relative motion between the printhead assembly and thesubstrate. This can be accomplished with a motion system, typically agantry or split axis XYZ system. Either the printhead assembly can moveover a stationary substrate (gantry style), or both the printhead andsubstrate can move, in the case of a split axis configuration. Inanother embodiment, a printhead assembly can be substantiallystationary; for example, in the X and Y axes, and the substrate can movein the X and Y axes relative to the printheads, with Z axis motionprovided either by a substrate support apparatus or by a Z-axis motionsystem associated with a printhead assembly. As the printheads moverelative to the substrate, droplets of ink are ejected at the correcttime to be deposited in the desired location on a substrate. A substratecan be inserted and removed from the printer using a substrate loadingand unloading system. Depending on the printer configuration, this canbe accomplished with a mechanical conveyor, a substrate floatation tablewith a conveyance assembly, or a substrate transfer robot with endeffector.

With respect to FIG. 6, printing system base 2100, can include firstriser 2120 and second riser 2122, upon which bridge 2130 is mounted. Forvarious embodiments of OLED printing system 2000, bridge 2130 cansupport first X-axis carriage assembly 2301 and second X-axis carriageassembly 2302, which can control the movement of first printheadassembly 2501 and second printhead assembly 2502, respectively acrossbridge 2130. First printhead assembly 2501 can be housed in firstprinthead assembly enclosure 2503, while second printhead assembly 2502can be housed in second printhead assembly enclosure 2504. For variousembodiments of printing system 2000, first X-axis carriage assembly 2301and second X-axis carriage assembly 2302 can utilize a linear airbearing motion system, which are intrinsically low-particle generating.According to various embodiments of a printing system of the presentteachings, an X-axis carriage can have a Z-axis moving plate mountedthereupon. In FIG. 6, first X-axis carriage assembly 2301 is depictedwith first Z-axis moving plate 2310, while second X-axis carriageassembly 2302 is depicted with second Z-axis moving plate 2312. ThoughFIG. 6 depicts two carriage assemblies and two printhead assemblies, forvarious embodiments of OLED inkjet printing system 2000, there can be asingle carriage assembly and a single printhead assembly. For example,either of first printhead assembly 2501 and second printhead assembly2502 can be mounted on an X,Z-axis carriage assembly, while a camerasystem for inspecting features of substrate 2050 can be mounted on asecond X,Z-axis carriage assembly.

In FIG. 6, each printhead assembly, such as first printhead assembly2501 and second printhead assembly 2502 of FIG. 6, can have a pluralityof printheads mounted in at least one printhead device, as depicted inpartial view for first printhead assembly 2501, which depicts aplurality of printhead devices 2505, each printhead device having one ormore printheads; e.g. nozzle printing, thermal jet or ink-jet type. Aprinthead device can include, for example, but not limited by, fluidicand electronic connections to at least one printhead; each printheadhaving a plurality of nozzles or orifices capable of ejecting ink at acontrolled rate, velocity and size. For various embodiments of printingsystem 2000 of the present teachings, one or more printheads of one ormore printhead devices 2505 can be configured to deposit one or morepatterned organic layers on the substrate 2050 in a “face up”configuration of the substrate 2050. Such layers can include one or moreof an electron injection or transport layer, a hole injection ortransport layer, a blocking layer, or an emission layer, for example.Such materials can provide one or more electrically functional layers.For various embodiments of printing system 2000, a printhead assemblycan include between about 1 to about 60 printhead devices, where eachprinthead device can have between about 1 to about 30 printheads in eachprinthead device. A printhead, for example, an industrial inkjet head,can have between about 16 to about 2048 nozzles, which can expel adroplet volume of between about 0.1 pL to about 200 pL.

According to various embodiments of a gas enclosure systems of thepresent teachings, given the sheer number of printhead devices andprintheads, first printhead management system 2701 and second printheadmanagement system 2702 can be housed in an auxiliary enclosure, whichcan be isolated from a printing system enclosure during a printingprocess for performing various measurement and maintenance tasks withlittle or no interruption to the printing process. First printheadmanagement system 2701 can be mounted upon first printhead managementplatform 2703, while second printhead management system 2702 can bemounted upon first printhead management platform 2704. As depicted inFIG. 6, first printhead assembly 2501 can be positioned relative tofirst printhead management system 2701 in order to perform variousmeasurement and maintenance procedures that can be provided by firstprinthead management system apparatuses 2707, 2709 and 2711.Additionally, second printhead assembly 2502 can be positioned relativeto second printhead management system 2702 in order to perform variousmeasurement and maintenance procedures that can be provided by secondprinthead management system apparatuses 2708, 2710 and 2712. Firstprinthead management system apparatuses 2707, 2709, and 2011 can bemounted on linear rail motion system 2705 for positioning relative tofirst printhead assembly 2501. Second printhead management systemapparatuses 2708, 2710, and 2012 can be mounted on linear rail motionsystem 2706 for positioning relative to second printhead assembly 2502.Apparatuses 2707, 2709, and 2011 of first printhead assembly 2701 andapparatuses 2708, 2710 and 2712 of second printhead assembly 2702 can beany of a variety of subsystems or modules for performing variousprinthead management functions. For example apparatuses 2707, 2709, and2011 of first printhead assembly 2701 and apparatuses 2708, 2710 and2712 of second printhead assembly 2702 can be any of a drop measurementmodule, a printhead replacement module, a purge basin module, and ablotter module.

For OLED printing system 2000 of FIG. 6, various embodiments of aprinting system can include substrate floatation table 2200, supportedby substrate floatation table base 2220. Substrate floatation table base2220 can be mounted on printing system base 2100. Various embodiments ofprinting system 2000 of FIG. 6 can have first isolator set 2110 (secondisolator of first isolator set on opposing side not shown) and secondisolator set 2112 (second isolator of second isolator set on opposingside not shown) Substrate floatation table 2200 of OLED printing systemcan support substrate 2050, as well as defining the travel over whichsubstrate 2050 can be moved through gas enclosure assembly 1000 duringthe printing of an OLED substrate. A Y-axis motion system of the presentteachings can include first Y-axis track 2351 and second Y-axis track2352, which can include a gripper system (not shown) for holding asubstrate. Y-axis motion can be provided by either a linear air bearingor linear mechanical system. In that regard, in conjunction with amotion system; as depicted in FIG. 6, a Y-axis motion system, substratefloatation table 2200 can provide frictionless conveyance of substrate2050 through a printing system.

In reference to FIG. 7, printing system 2001 can have all of theelements previously described for printing system 2000 of FIG. 6. Forexample, but not limited by, printing system 2001 of FIG. 7 can haveservice bundle housing exhaust system 2400 for containing and exhaustingparticles generated from a service bundle. Service bundle housingexhaust system 2400 of printing system 2001 can include service bundlehousing 2410, which can house a service bundle. According to the presentteachings, a service bundle can be operatively connected to a printingsystem to provide various optical, electrical, mechanical and fluidicconnections required to operate various devices and apparatuses in a gasenclosure system, for example, but not limited by, various devices andapparatuses associated with a printing system. Printing system 2001 ofFIG. 7 can have substrate support apparatus 2250 for supportingsubstrate 2050, which can be positioned with precision in the Y-axisdirection using Y-axis positioning system 2355. Both substrate supportapparatus 2250 and Y-axis positioning system 2355 are supported byprinting system base 2101. Substrate support apparatus 2250 can bemounted on Y-axis motion assembly 2355 and can be moved on rail system2360 using, for example, but not limited by, a linear bearing system;either utilizing mechanical bearings or air bearings. For variousembodiments of gas enclosure systems, an air bearing motion system helpsfacilitation frictionless conveyance in the Y-axis direction for asubstrate placed on substrate support apparatus 2250. Y-axis motionsystem 2355 can also optionally use dual rail motion, once again,provided by a linear air bearing motion system or a linear mechanicalbearing motion system.

Regarding motion systems supporting various carriage assemblies of thepresent teachings, such as printing system 2000 of FIG. 6 and printingsystem 2001 of FIG. 7 can have a first X-axis carriage that can be usedfor mounting a printhead assembly and a second carriage assembly thatcan be used to mount a variety of various assemblies, such as a cameraassembly. For example, in FIG. 7, orienting system 2001 can haveassembly 2300A that is depicted having printhead assembly 2500 mountedthereupon and second X-axis carriage assembly 2300B that is depictedhaving camera assembly 2550 mounted thereupon. Substrate 2050, which ison substrate support apparatus 2250, can be located in various positionsproximal to bridge 2130, for example, during a printing process.Substrate support apparatus 2250 can be mounted on printing system base2101. In FIG. 7, printing system 2001 can have first X-axis carriageassembly 2300A and second X-axis carriage assembly 2300B mounted onbridge 2130. First X-axis carriage assembly 2300A can also include firstZ-axis moving plate 2310A for the Z-axis positioning of printheadassembly 2500, while second X-axis carriage assembly 2300B can havesecond Z-axis moving plate 2310B for the Z-axis positioning of cameraassembly 2550. In that regard, various embodiments of carriageassemblies 2300A and 2300B can provide precision X,Z positioning withrespect to a substrate positioned on substrate support 2250 forprinthead assembly 2500 and camera assembly 2550, respectively. Forvarious embodiments of printing system 2001, first X-axis carriageassembly 2300A and second X-axis carriage assembly 2300B can utilize alinear air bearing motion system, which is intrinsically low-particlegenerating.

A camera assembly 2550 can include camera 2552, camera mount assembly2554 and lens assembly 2556. Camera assembly 2550 can be mounted tomotion system 2300B on Z-axis moving plate 2310B, via camera mountassembly 2556. Camera 2552 can be any image sensor device that convertsan optical image into an electronic signal, such as by way ofnon-limiting example, a charge-coupled device (CCD), a complementarymetal-oxide-semiconductor (CMOS) device or N-typemetal-oxide-semiconductor (NMOS) device. Various image sensor devicescan be configured as an array of sensors for an area scan camera, or asingle row of sensors, for a line scan camera. Camera assembly 2550 canbe connected to image processing system that can include, for example, acomputer for storing, processing, and providing results. As previouslydiscussed herein for printing system 2001 of FIG. 7, Z-axis moving plate2310B can controllably adjust the Z-axis position of camera assembly2550 relative to substrate 2050. During various processes, such as forexample, printing and data collection, substrate 2050 can becontrollably positioned relative to the camera assembly 2550 using theX-axis motion system 2300B and Y-axis motion system 2355.

Various camera assemblies can utilize cameras having differentcapabilities. In various embodiments, camera assembly 2550 of FIG. 7 canbe a high-speed, high-resolution camera. In various embodiments ofsystems and methods of the present teachings, a line scan camera havingabout 8192 pixels, with a working height of about 190 mm, and capable ofscanning at about 34 kHz can be used. In various embodiments of systemsand methods of the present teachings, more than one camera can bemounted on an X-axis carriage assembly for various embodiments of aprinting system substrate camera assembly, where each camera can havedifferent specifications regarding field of view and resolution. Forexample, one camera can be a line scan camera for in situ particleinspection, while a second camera can be for regular navigation of asubstrate in a gas enclosure system. Such a camera useful for regularnavigation can be an area scan camera having a field of view in therange of about 5.4 mm×4 mm with a magnification of about 0.9× to about10.6 mm×8 mm with a magnification of about 0.45×. In still otherembodiments, one camera can be a line scan camera for in situ particleinspection, while a second camera can be for precise navigation of asubstrate in a gas enclosure system, for example, for substratealignment. Such a camera can be useful for precise navigation can be anarea scan camera having a field of view of about 0.7 mm×0.5 mm with amagnification of about 7.2×. Various embodiments of a printing systemaccording to the present teachings may have one or more cameras mountedto an X-axis carriage assembly for the purpose of, for example,inspecting various thin film layers that can be printed on anoptoelectronic device, as previously described for FIG. 1.

FIG. 8 is a schematic diagram showing a gas enclosure system 500.Various embodiments of a gas enclosure system 500 according to thepresent teachings can comprise, for example gas enclosure 4510 of FIG. 4for various modules and chambers as described for FIG. 5. Forillustrative purposes, FIG. 8 will refer to gas enclosure 4510 of FIG. 4for housing a printing system, though it is to be understood that theseteachings apply to a broad number of enclosures, modules and chambers ofthe present teachings.

Gas purification loop 3130 can be in fluid communication gas enclosure4510, and at least one thermal regulation system 3140. Additionally,various embodiments of gas enclosure system 500 can have pressurizedinert gas recirculation system 3000, which can supply inert gas foroperating various devices, such as a substrate floatation table for anOLED printing system. Various embodiments of a pressurized inert gasrecirculation system 3000 can utilize a compressor, a blower andcombinations of the two as sources for various embodiments ofpressurized inert gas recirculation system 3000, as will be discussed inmore detail subsequently herein. Additionally, gas enclosure system 500can have a circulation and filtration system internal to gas enclosuresystem 500 (not shown).

As depicted in FIG. 8, for various embodiments of a gas enclosureassembly according to the present teachings, the design of a filtrationsystem can separate the inert gas circulated through gas purificationloop 3130 from the inert gas that is continuously filtered andcirculated internally for various embodiments of gas enclosure assembly1101. Gas purification loop 3130 includes outlet line 3131 from gasenclosure 4510 of FIG. 4, to a solvent removal component 3132 and thento gas purification system 3134. Inert gas purified of solvent and otherreactive gas species, such as oxygen and water vapor, are then returnedto gas enclosure 4510 through inlet line 3133. Gas purification loop3130 may also include appropriate conduits and connections, and sensors,for example, oxygen, water vapor and solvent vapor sensors. A gascirculating unit, such as a fan, blower or motor and the like, can beseparately provided or integrated, for example, in gas purificationsystem 3134, to circulate gas through gas purification loop 3130.According to various embodiments of gas enclosure assembly 1101, thoughsolvent removal system 3132 and gas purification system 3134 are shownas separate units in the schematic shown in FIG. 8, solvent removalsystem 3132 and gas purification system 3134 can be housed together as asingle purification unit.

Gas purification loop 3130 of FIG. 8 can have solvent removal system3132 placed upstream of gas purification system 3134, so that inert gascirculated from gas enclosure 4510 of FIG. 4 passes through solventremoval system 3132 via outlet line 3131. According to variousembodiments, solvent removal system 3132 may be a solvent trappingsystem based on adsorbing solvent vapor from an inert gas passingthrough solvent removal system 3132 of FIG. 8. A bed or beds of asorbent, for example, but not limited by, such as activated charcoal,molecular sieves, and the like, may effectively remove a wide variety oforganic solvent vapors. For various embodiments of a gas enclosuresystem cold trap technology may be employed to remove solvent vapors insolvent removal system 3132. As previously discussed herein, for variousembodiments of a gas enclosure system according to the presentteachings, sensors, such as oxygen, water vapor and solvent vaporsensors, may be used to monitor the effective removal of such speciesfrom inert gas continuously circulating through a gas enclosure system,such as gas enclosure system 500 of FIG. 8. Various embodiments of asolvent removal system can indicate when sorbent, such as activatedcarbon, molecular sieves, and the like, has reached capacity, so thatthe bed or beds of sorbent can be regenerated or replaced. Regenerationof a molecular sieve can involve heating the molecular sieve, contactingthe molecular sieve with a forming gas, a combination thereof, and thelike. Molecular sieves configured to trap various species, includingoxygen, water vapor, and solvents, can be regenerated by heating andexposure to a forming gas that comprises hydrogen, for example, aforming gas comprising about 96% nitrogen and 4% hydrogen, with saidpercentages being by volume or by weight. Physical regeneration ofactivated charcoal can be done using a similar procedure of heatingunder an inert environment.

Any suitable gas purification system can be used for gas purificationsystem 3134 of gas purification loop 3130 of FIG. 8. Gas purificationsystems available, for example, from MBRAUN Inc., of Statham, N.H., orInnovative Technology of Amesbury, Mass., may be useful for integrationinto various embodiments of a gas enclosure assembly according to thepresent teachings. Gas purification system 3134 can be used to purifyone or more inert gases in gas enclosure system 500, for example, topurify the entire gas atmosphere within gas enclosure assembly 1101. Aspreviously discussed herein, in order to circulate gas through gaspurification loop 3130, gas purification system 3134 can have a gascirculating unit, such as a fan, blower or motor, and the like. In thatregard, a gas purification system can be selected depending on thevolume of the enclosure, which can define a volumetric flow rate formoving an inert gas through a gas purification system. For variousembodiments of gas enclosure system having a gas enclosure assembly witha volume of up to about 4 m³; a gas purification system that can moveabout 84 m³/h can be used. For various embodiments of gas enclosuresystem having a gas enclosure assembly with a volume of up to about 10m³; a gas purification system that can move about 155 m³/h can be used.For various embodiments of a gas enclosure assembly having a volume ofbetween about 52-114 m³, more than one gas purification system may beused.

Any suitable gas filters or purifying devices can be included in the gaspurification system 3134 of the present teachings. In some embodiments,a gas purification system can comprise two parallel purifying devices,such that one of the devices can be taken off line for maintenance andthe other device can be used to continue system operation withoutinterruption. In some embodiments, for example, the gas purificationsystem can comprise one or more molecular sieves. In some embodiments,the gas purification system can comprise at least a first molecularsieve, and a second molecular sieve, such that, when one of themolecular sieves becomes saturated with impurities, or otherwise isdeemed not to be operating efficiently enough, the system can switch tothe other molecular sieve while regenerating the saturated ornon-efficient molecular sieve. A control unit can be provided fordetermining the operational efficiency of each molecular sieve, forswitching between operation of different molecular sieves, forregenerating one or more molecular sieves, or for a combination thereof.As previously discussed herein, molecular sieves may be regenerated andreused.

Thermal regulation system 3140 of FIG. 8 can include at least onechiller 3142, which can have fluid outlet line 3141 for circulating acoolant into gas enclosure assembly 1101, and fluid inlet line 3143 forreturning the coolant to the chiller. An at least one fluid chiller 3142can be provided for cooling the gas atmosphere within gas enclosuresystem 500. For various embodiments of a gas enclosure system of thepresent teachings, fluid chiller 3142 delivers cooled fluid to heatexchangers within the enclosure, where inert gas is passed over afiltration system internal the enclosure. At least one fluid chiller canalso be provided with gas enclosure system 500 to cool heat evolvingfrom an apparatus enclosed within gas enclosure system 500. For example,but not limited by, at least one fluid chiller can also be provided forgas enclosure system 500 to cool heat evolving from an OLED printingsystem. Thermal regulation system 3140 can comprise heat-exchange orPeltier devices and can have various cooling capacities. For example,for various embodiments of a gas enclosure system, a chiller can providea cooling capacity of from between about 2 kW to about 20 kW. Variousembodiments of a gas enclosure system can have a plurality of fluidchillers that can chill one or more fluids. In some embodiments, thefluid chillers can utilize a number of fluids as coolant, for example,but not limited by, water, anti-freeze, a refrigerant, and a combinationthereof as a heat exchange fluid. Appropriate leak-free, lockingconnections can be used in connecting the associated conduits and systemcomponents.

The present teachings are intended to be illustrative, and notrestrictive. The Abstract is provided to comply with 37 C.F.R. §1.72(b),to allow the reader to quickly ascertain the nature of the technicaldisclosure. It is submitted with the understanding that it will not beused to interpret or limit the scope or meaning of the claims. Also, inthe above Detailed Description, various features may be grouped togetherto streamline the disclosure. This should not be interpreted asintending that an unclaimed disclosed feature is essential to any claim.Rather, inventive subject matter may lie in less than all features of aparticular disclosed embodiment. Thus, the following claims are herebyincorporated into the Detailed Description as examples or embodiments,with each claim standing on its own as a separate embodiment, and it iscontemplated that such embodiments can be combined with each other invarious combinations or permutations. The scope of the invention shouldbe determined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

What is claimed is:
 1. An ink composition comprising: 75-95 wt. % of apolyethylene glycol dimethacrylate monomer, a polyethylene glycoldiacrylate monomer, or a combination thereof, wherein the polyethyleneglycol dimethacrylate monomer and the polyethylene glycol diacrylatemonomer have number average molecular weights in the range from about230 g/mole to about 430 g/mole; 4-10 wt. % of pentaerythritoltetraacrylate, pentaerythritol tetramethacrylate, or a combinationthereof; and 1-15 wt. % of a spreading modifier having a viscosity inthe range from about 14 to about 18 cps at 22° C. and a surface tensionin the range from about 35 to about 39 dynes/cm at 22° C.
 2. The inkcomposition of claim 1, wherein the spreading modifier has a viscosityin the range from about 14 to about 16 cps at 22° C. and a surfacetension in the range from about 35 to about 38 dynes/cm at 22° C.
 3. Theink composition of claim 1, wherein the spreading modifier comprises analkoxylated aliphatic diacrylate monomer, an alkoxylated aliphaticdimethacrylate monomer, or a combination thereof.
 4. The ink compositionof claim 2, wherein the spreading modifier comprises an alkoxylatedaliphatic diacrylate monomer, an alkoxylated aliphatic dimethacrylatemonomer, or a combination thereof.
 5. The ink composition of claim 1,characterized in that: the spreading modifier has a maximum stableinkjet jetting frequency of at least 23 kHz at 22° C.; and the spreadingmodifier has a maximum drop volume variation of no greater than 15% anda maximum drop velocity variation of no greater than 15% up to itsmaximum stable inkjet jetting frequency at 22° C.
 6. The ink compositionof claim 1 having a maximum stable inkjet jetting frequency of at least25 kHz at 25° C.
 7. The ink composition of claim 1, further comprising acrosslinking photoinitiator present in an amount that results in avolume change of no greater than 1% when a film printed from the inkcomposition is cured.
 8. The ink composition of claim 7, wherein thephotoinitiator is 2,4,6-trimethylbenzoyl-diphenylphosphine oxide.
 9. Theink composition of claim 8, wherein the2,4,6-trimethylbenzoyl-diphenylphosphine oxide is present in an amountin the range from about 3.75 to about 4.25 wt. % of the ink composition.10. The ink composition of claim 3, wherein the photoinitiator is2,4,6-trimethylbenzoyl-diphenylphosphine oxide.
 11. The ink compositionof claim 10, comprising 75-95 wt. % of a polyethylene glycoldimethacrylate monomer having a number average molecular weight of about330 g/mole, and 4-10 wt. % of the pentaerythritol tetraacrylate, whereinthe spreading modifier comprises the alkoxylated aliphatic diacrylatemonomer.
 12. A process of forming a polymeric thin film layer on asubstrate, the method comprising: providing an inert processingenvironment; providing an OLED device substrate having an inorganic thinfilm formed thereupon; providing an ink composition comprising: 75-95wt. % of a polyethylene glycol dimethacrylate monomer, a polyethyleneglycol diacrylate monomer, or a combination thereof, wherein thepolyethylene glycol dimethacrylate monomer and the polyethylene glycoldiacrylate monomer have number average molecular weights in the rangefrom about 230 g/mole to about 430 g/mole; 4-10 wt. % of pentaerythritoltetraacrylate, pentaerythritol tetramethacrylate, or a combinationthereof; 1-15 wt. % of a spreading modifier having a viscosity in therange from about 14 to about 18 cps at 22° C. and a surface tension inthe range from about 35 to about 39 dynes/cm at 22° C.; and 0.1-5 wt. %of a photoinitiator, printing a layer of the ink composition over adefined area of the substrate including the inorganic thin film, andcuring the layer of printed ink, wherein an organic polymeric thin filmis formed over the inorganic thin film.
 13. The process of claim 12,wherein the spreading modifier comprises an alkoxylated aliphaticdiacrylate monomer, an alkoxylated aliphatic dimethacrylate monomer, ora combination thereof.
 14. The process of claim 12, wherein the volumedifference between the layer of printed ink composition and the organicpolymeric thin film is no greater than 1%.
 15. The process of claim 12,wherein the volume difference between the layer of printed inkcomposition and the organic polymeric thin film is no greater than 0.5%.16. The process of claim 12, wherein the photoinitiator is2,4,6-trimethylbenzoyl-diphenylphosphine oxide.
 17. The process of claim13, wherein the photoinitiator is2,4,6-trimethylbenzoyl-diphenylphosphine oxide.
 18. The process claim12, further comprising before the step of providing an OLED devicesubstrate: providing an industrial printing system housed within theinterior of a gas enclosure, wherein the industrial printing systemcomprises: a printhead assembly comprising at least one printhead; asubstrate support system for supporting a substrate; and a motion systemfor the precise positioning of the substrate relative to the printheadassembly; and a UV curing module.
 19. The process of claim 12, whereinthe inert process environment is provided using an inert gas selectedfrom nitrogen, any of the noble gases, and combinations thereof.
 20. Theprocess of claim 12, wherein the inert process environment has watervapor content and oxygen content each at less than 100 ppm.